1. Field of the Invention
The present invention relates to a semiconductor pressure sensor of an improved structure which may be used in vehicles or the like. The present invention also relates to a method of manufacturing such a sensor.
2. Description of the Related Art
A conventional semiconductor pressure sensor is shown, in section, in FIG. 1. As shown in the drawing, an outer package 2 has a pressure introduction port 1. The outer package 2 accommodates a package 4 of a pressure sensor itself (hereinafter simply referred to as "package"), the package 4 being mounted on a ceramic substrate 3. A stem 5, including a pressure introduction pipe, is provided at the bottom of the package 4, with the pipe communicating with the pressure introduction port 1 of the outer package 2. A pressure sensor chip 7, which is joined to a glass mount 6 by anodic bonding, is disposed in the package 4, with the reverse surface of the chip 7 facing the pressure introduction port 1. The pressure sensor chip 7 is electrically connected, via wire leads 8 and leads 9, to conductive patterns 10 formed on the ceramic substrate 3. A vacuum prevails inside the package 4. An IC chip 11, such as a flip chip, is electrically connected to the conductor patterns 10 via bumps 12. The conductor patterns 10 are electrically connected, via outer leads 13, to a circuit outside the semiconductor pressure sensor.
The conventional semiconductor pressure sensor having the above-described construction is manufactured in the following manner. First, the pressure sensor chip 7 and the glass mount 6 are bonded together by anodic bonding, and the resultant body is die-bonded to the stem 5. Subsequently, the pressure sensor chip 7 and the leads 9 are connected by the wire leads 8. Thereafter, the pressure within the package 4 is reduced to a vacuum within, thereby forming a vacuum chamber 14. The thus obtained package 4 and the IC chip 11 are mounted on the ceramic substrate 3. Thereafter, the ceramic substrate 3 with the package 4 and the IC chip 11 is incorporated into the outer package 2, thereby completing the semiconductor pressure sensor.
The semiconductor pressure sensor is used in the following manner. The pressure of the gas to be measured is introduced from the pressure introduction port 1, which pressure is then received by the reverse surface of the pressure sensor chip 7. Since the front surface of the pressure sensor chip 7 is exposed the vacuum within the chamber 14, the output of the pressure sensor chip 7 is an absolute-pressure output. The sensor output is amplified by an amplification circuit, such as that shown in FIG. 2, so as to obtain a signal output. In FIG. 2, reference numerals 7 and 11 respectively denote circuits formed in the pressure sensor chip 7 and the IC chip 11.
The conventional semiconductor pressure sensor entails the following problem. Since assembly is performed in two stages, that is, the assembly of the package 4 first, then the mounting of the package 4 and the IC chip 11 on the ceramic substrate 3, the required manufacturing processes are inevitably complicated and time-consuming. For instance, the vacuum chamber must be formed with a high level of precision.